This invention relates to a three-port lumped-element circulator.
A circulator of the type described is often used in a microwave communication system and comprises three ports, at least one ferrimagnetic piece, a magnet for producing a stationary magnetic field in the adjacency of the ferrimagnetic piece or pieces to magnetically stationarily bias the same, and an assembly of lumped-element conductors connected on the ferrimagnetic piece to the ports. An input microwave signal supplied to one of the ports that is selected as an input port is circulated to one of the two remaining ports that is predetermined as an output port. As will later be described with one of several figures of the accompanying drawing, the lumped-element conductor assembly of a conventional circulator of the type specified consists of three elongate conductor members. Each of the conductor members has a first wide conductor on one end thereof to serve as one of the ports, a pair of thin conductors extended parallel from the wide conductor to be intertwined with the thin conductors of two other conductor members on a center area of the ferrimagnetic piece, and a second wide conductor uniting the two thin conductors on the other end of the conductor member. The thin conductors are weak against the mechanical shock and liable to break during assembly of the circulator. Moreover, it is inevitable that another ferrimagnetic piece, if used, is appreciably spaced from the ferrimagnetic piece on which the assembly is arranged. As will also later be described with reference to another of the several figures, the conductor assembly of another conventional circulator disclosed by R. H. Knerr in U.S. Pat. No. 3,716,805 consists of a single ring-shaped conductor. Each portion of the single conductor that is connected to two adjacent ports serve as a lumped-element conductor. The single conductor is strong against shock, facilitates manufacture of the circulator, and enables another ferrimagnetic piece, when used, to be brought close to the ferrimagnetic piece that is indispensable as the circulator. It is, however, difficult to achieve a wide operable band width with the conventional circulators.